Having a "rainy day" fund is always a good idea.  It is generally a savings fund/account that you keep separate from other savings and only use when absolutely necessary.  Did you know...

• No matter what your age, you’ll improve your financial security with a “rainy day” fund.
• Nearly everybody should try to build up savings of at least three to six months’ income.
• Financial “rainy days” can be caused by anything from major car repairs to unexpected dental work.
• Your “rainy day” fund not only protects you; it can earn interest and grow significantly over time.
• As your fund grows, consider shifting the extra money into longer-term investments for your retirement.
• Make sure your money is in an easily accessible account such as a basic savings or money market account. 
• The best savers tend to be Generation Xers, who save more of their money than the baby boomers.